Oct 08, 2026 by Offer

BNP Paribas Technical Interview 2027: String Array Question & Solution

For the BNP Paribas technical interview question "Find the largest common prefix among an array of strings," the clean solution is vertical scanning: take the first string as reference, compare character by character across all strings, and stop at the first mismatch. Here is how to tackle the bnp paribas largest common prefix, step by step.

What the BNP Paribas Largest Common Prefix Question Assesses

Classic algorithm questions like this are commonly reported by candidates for technology roles at BNP Paribas. The interviewer is testing structured problem-solving in code: can you pick an efficient approach, reason about complexity, and handle edge cases without prompting? Candidates commonly report that the discussion around the solution — trade-offs and edge cases — matters as much as the code itself.

How to Solve the BNP Paribas Largest Common Prefix Question

Follow four steps: approach, complexity, edge cases, code.

Step 1 — Approach: Vertical scanning. Use the first string as the reference; for each character position, check that every other string has the same character there. The common prefix ends at the first position where any string differs or ends.
Step 2 — Complexity: Time is O(S) where S is the total characters examined — in the worst case every character of every string; space is O(1) extra beyond the result. Mention the alternative (sorting first, then comparing only first and last) and why vertical scanning is simpler.
Step 3 — Edge cases: Empty array (return empty string), array containing an empty string (prefix is empty), single string (the string itself), and strings where one is a prefix of another.
Step 4 — Code it cleanly: Loop positions over the first string; inner loop over the remaining strings; break on mismatch or end-of-string; return the slice. Narrate as you write.

Example line: "I would vertically scan: for each character position in the first string, verify all other strings match at that position, stopping at the first mismatch — that is O(total characters) time with constant extra space, and it handles empty inputs naturally."

Common Mistakes With the BNP Paribas Largest Common Prefix Question

Jumping to code without stating the approach. Candidates commonly report that interviewers want the plan first — coding silently hides your thinking and wastes the chance to show structure.
Missing edge cases. Empty array and empty strings are the classic probes. Stating them upfront shows professional coding habits.
No complexity analysis. "It works" is not enough — always state time and space complexity unprompted. It is the cheapest way to signal seniority.

Algorithm questions are as much about communication as correctness. Narrate your approach, flag the edge cases, analyse complexity, then write clean code — that sequence is what interviewers score.

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FAQ

Is vertical scanning the best approach? It is the standard optimal answer — simple and O(S). The sort-based alternative is also O(S log n)-ish with more overhead; mentioning it shows awareness without overcomplicating.

What if I blank on the approach? Start with brute force aloud, then optimise. Interviewers reward visible reasoning over silent perfection — talk through what you are trying.

Should I test my code? Yes — walk through one example ("flower", "flow", "flight" → "fl") and one edge case. Tracing catches bugs and demonstrates diligence.

Preparing for BNP Paribas's interview? Our 2027 BNP Paribas Online Test and Pymetrics Test Tutorials has practice questions and answers — $79 one-time, instant download.